Leland J. Haworth, 74, a noted physicist who was a former director of the National Science Foundation and a member of the Atomic Energy Commission, died of cancer Monday in Port Jefferson, L. I.

He was head of the foundation from 1963 to 1969. A federal agency, it is the government's chief promoter of basic research and education in the sciences.

Dr. Haworth was director of the Brookhaven National Laboratory in Upton, Long Island, when he was tapped by president John F. Kennedy in 1961 to become a member of the old Atomic Energy Commission.

He had joined Brookhaven in 1947, became its director a year later and in 1951 was named vice president of Associated Universities Inc., which operates Brookhaven for the federal government. He became AUI president in 1961.

Dr. Haworth specialized in study and research in secondary electronic emission, low temperatures, nuclear physics, high energy physics and electronics.

From 1941 to 1945, he was on leave from the University of Illinois to do defense work at the Massachusetts Institute of Technology Radiation Laboratory. He received the President's Certificate of Merit for his World War II research.

For two years before he was named to the AEC, he was on the board of directors of the Oak Ridge Institute for Nuclear Studies at the AEC Oak Ridge National Laboratory in Tennessee.

Dr. Haworth was born in Flint, Mich. He held bachelor's and master's degrees from the University of Indiana and a doctorate from the University of Wisconsin. He began as a high school teacher in Indianapolis and went on to teach physics at the University of Wisconsin and the University of Illinois.

After he left the National Science Foundation, Dr. Haworth returned to Associated Universities, Inc., as a special assistant to the president. He retired in 1975.

He had served with a number of groups and committees formed to advise the Department of Defense and other government agencies. He was the author of numerous papers in his field.

Dr. Haworth was a former president of the American Nuclear Society, of which he was a fellow. He also was a fellow of the American Physical Society and a member of the National Academy of Sciences, the American Philosophical Society, the American Academy of Arts and Sciences, Phi Beta Kappa and the Cosmos Club.

He is survived by his wife, Irene Benik Haworth, of the home in Belle Terre, Port Jefferson; two children by a previous marriage, Barbara J. Beck, of Daytona Beach, Fla., and John J. Haworth of Attleboro, Mass.; a sister, Anna R. Wallace, of Bloomington, Ind., and four grandchildren.